1. Field of the Invention
The invention relates to welding and refers more specifically to a structure for and method of resistance welding using an inductively coupled power source to heat the material to be welded by current and/or magnetic hysteresis induced therein.
2. Description of the Prior Art
The resistance welding process is commonly used to make spot or seam welds to join sheet metal parts. In the resistance welding process of the past, electrodes usually made of copper have been used to apply large amounts of current to a weld coupling in order to heat the metal to the point where it softens and may be forged together by pressure. The pressure for forging the parts together has been applied through the same welding electrodes which have applied the current to the material to be welded in the past.
Seam welding in the past has been performed in a manner similar to spot welding. In seam welding however the electrodes have usually been in the shape of wheels which are rolled along the parts to be welded as the weld is being made. Prior art spot welding and seam or continuous welding structures are illustrated in FIGS. 1 and 2 respectively.
The power source for the current used to heat the metal in the past has generally been a low voltage output transformer or direct current power source. The transformers used for resistance welding usually put out voltages of between two and twenty volts at currents of between five thousand and fifty thousand amps.
As a result of the currents involved resistance welding transformers of the past have usually been large and heavy and relatively costly due to the amount of iron and copper required to construct them. A resistance welding transformer of the past has usually weighed several hundred pounds, although smaller transformers weighing only fifty pounds have been made to work in some specialized applications. Most resistance welding transformers require water cooling.
Another problem related to resistance welding is getting the current from the transformer (or DC power supply) to the welding electrodes. Because of the size and weight of the normal transformer of the past, it has often been impossible to place the transformer close to the welding electrodes. Large cables have been required to handle the welding currents and keep energy losses to a minimum. Often these cables are water cooled. The cables add cost and complexity to a welding system and are usually the least reliable part of the system.